Relative displacement of the implant with respect to bone and quality of bone-implant contact play critical roles in the dental implant stability. The goal of this study was to investigate the dental implant stability using non-linear finite elements method. Therefore, bone-implant relative displacement due to applied force to the implant was calculated, and then an appropriate factor for defining quality of bone-implant contact was presented. In order to develop a three dimensional model and compare the results with clinical studies, computed tomography (CT) scan data of a rabbit tibia was considered as a base. The model was exported to ABAQUS 6.9-1 to be analyzed using nonlinear finite elements method. Dynamic analysis was done on the model using the proper boundary condition and dynamic loads. Force-displacement curves in bone-implant interface were nonlinear. Friction coefficient, which is a criterion for implant stability and relative displacement, approximately became doubled as the vertical contact force was halved. However, the friction coefficient decreased with reduction of coulomb frictional coefficient. Friction coefficient, which is calculated upon force-displacement curves, could be considered as a criterion to evaluate the dental implant stability. Decrease of the vertical contact force and also using rough surfaces improved the quality of bone-implant contact and stability of dental implant.

In this research, dynamic behavior of non-linear finite element model of a drillstring is investigated. By considering total length of drillstring, a three-dimensional timoshenko beam element is employed. In addition the geometric stiffening effect, the added fluid mass and the contact between different parts of the drillstring and the borehole wall has been considered, with a complete model the effects of these factors have been analyzed separately. The equation of motion obtained and full order equations are used to drive the results. For the first time, a domain of drillstring that contact more possibility to occur in this domain is identified. The natural frequencies of the drillstring are evaluated and compared with the available commercial software results and recorded results for the actual drillstring. Coupling of vibrations of model is tested and the effect of linear and non-linear model in analysis of dynamic behavior and vibration of drillstring, especially in contact with the borehole wall and the effect of weight on bit change on the contact at stabilizers are analyzed and for the first time the contact time in each of stabilizers have been evaluated.

Vibration of drillstring is the most important factor of its destruction and reduction in drilling operations efficiency. One of the main causes of excessive vibration of drillstring is drillstring-wellbore contact, therefore drillstring-wellbore contact has been studied in several researches. Indeed the contact behavior of drillstring and wellbore is of great concern to drilling companies in the oil and gas exploration industries. In this research, dynamic behavior and vibration of non-linear finite element model of a drillstring in contact with wellbore, has been investigated. By considering total length of drillstring, a three-dimensional timoshenko beam element is employed. In addition the geometric stiffening effect including nonlinear terms, the added fluid mass and the contact between drillstring and borehole wall has been considered using improved contact model with a more complete model than previous studies, that the stiffeness of contact determined form energy balance relations. The equation of motion of drillstring obtained using energy approach and lagrange’s equations and full order equations are used to drive the results. Coupling between various vibrations has been tested and the effect of recent model in analysis of dynamic behavior and vibration of drillstring have been evaluated.

Earth as a dynamic system is constantly undergoing the Change and variation. The changes causing factors include a wide range of dynamic processes, which consist of tidal effects, the loading on the crust and tectonic activity of tectonic plates. Accumulation of strain energy at the boundary between the plates and the surrounding area of faults are the most important consequences of movement and deformation of the tectonic plates. This energy may causes tension forces in the fracture sits, and if these forces can overcome the rocks resistance, an earthquake will occur. To measure strain energy, some mechanical tools contain strain gauges and turnkey have been installed at faults location which measure the deformations in situ. Due to the high cost of purchasing and maintenance of such these devices, based on geodetic observation, some alternative methods have been developed for study of the earth crust in local scales. Today, time measurement of the earth's crust deformations has been recognized as one of the notable branches of geodesy.
Measuring the Earth's crust deformation by geodetic methods has significant impacts on geological studies and provides a deep insight into understanding the mechanism of tectonic activities such as earthquakes and volcanoes.
Over time, measurement methods in geodesy significantly expande and space measurement methods have been replaced classic geodetic observations. The Global Positioning System (GPS) playes an important role in the development of observational methods in geodesy. By using GPS observations, determining of three-dimensional positioning become possible in a Earth-fixed coordinate system. Therefore, by comparing the obtained positions in different epochs, displacement vector can be calculated. Displacement vectors are not suitable quantities for deformation geometric interpretation, because they must be determined in comparison with a constant basic coordinate system.
On the other hand, strain tensor can be calculated by using displacement vectors. This tensor contains invariant parameters of coordinate system and has a direct association with geometric interpretation of deformation.
Since Iran is a seismically active and has been located within the convergence zone of two rigid plates, the Arabian and Eurasian plates, It is known as a natural laboratory for studying the kinematics and dynamics of tectonic interactions. Considering these reasons, researchers aim to study the geodynamic network of Iran. The neotectonics of the Iranian plateau is complicated due to various tectonic processes, (Zagros, Alborz, Kopeh Dagh, and Talesh), subduction of the oceanic crust (Makran), and a transition zone between the Zagros fold-and-thrust belt and the subduction zone of Makran.
In this paper, using observations of GPS velocity vectors at the different station of Geodynamic network of IRAN, two-dimensional deformation of the earth crust was estimated by 2-D strain analysis within 2009 -2013. And then, in order to deformation interpretation, invariant geometric criteria like dilatation and maximum shear were evaluated.
In this regard, as the first step, coordinates of the all GPS stations was calculated in two observational epochs in global coordinate system. In addition, considering the proper map projection, the coordinates were transfered into the projection plane. In the next step, the apparent displacement vector was determined for each GPS station. Finally, using displacement vectors, strain tensor components as well as dilatation and maximum shear invariant parameters was computed for the whole Geodynamic network.
Strain tensor calculates by using displacement vector derivatives but geodetic observations, only provide the discrete values of the displacement in GPS stations. Using the data interpolation techniques such as finite element method is an appropriate way to solve this problem. In this method, the domian of the data point partitions into some smaller sub-domains and in each one, a smooth function fits in that domain by considering the specified constraints on the existing data point. In order to create a smooth surface through the data points there must be a smooth transition from one patch or element to another across all shared edges. Interpolating functions in each sub-domain must apply in some continuity conditions such as continuity of the function itself, the first or higher order derivative when passing between two adjacent elements.
Due to the nature of the Earth's crust and two-dimensional strain analysis; triangular element is the simplest geometric element in this study. In addition to determine the mathematical form of displacement function using discrete values of displacement, nonlinear finite element method was known as one of the most important point of this study. In this method, after an area meshing by Delaunay Triangular Element, C1 continuous interpolation was adopted.
The interpolating function (displacement vector) on each triangle was a rational function gained by blending three cubic polynomials that are known as the Cubic Bezier Triangular Patches. Thus, unlike the previous methods, in this case, the displacement vector in common boundary of the two adjacent Triangular elements had C1 continuity, so a smooth interpolation having C1 continuity in the entire GPS network (vertices of the triangle domain) is achievable.
Since we are working with triangles, we will utilize barycentric coordinates rather than Cartesian coordinates. So the Bezier Triangular patches (displacement vector) or Bezier triangles were defined by Bezier ordinates or control points in barycentric coordinates form.
For our interpolating problem, only numerical values of displacement vector at the three vertices of the domain triangle was provided. So the inner control points of the control mesh (unknown Bezier ordinates) must be determined. This can be done if information about the gradient or normal on the control points is given. Least Squares Minimization Method based on Finite Difference Techniques was helpful for prescribing the first order derivatives of displacement function at the vertices of each triangle for creating a C1 surface. The number of vertices around the data point is chosen by the minimum distance technique.
According to the conducted analysis, the maximum amount of shear quantity equals to 5.58×10-5 unit/year value in the southern parts of Iran. The maximum amount of dilatation quantity equals to the -2.89×10-4 unit/year value in the southeast of the country, which represents a net contraction in these areas. This contraction demonstrates the collision of the Arabian plate from the southwest to Eurasian from the Northeast, and confirms the reverse and strike-slip faults in the Iranian plateau. Also the result of the computation and the evaluations by comparison with the seismic map of the region show the success and usefulness of the presented method for deformation study of the curst.

In the present paper, applicability of the modified fixed grid finite element method in solution of three dimensional elasticity problems of functionally graded materials is investigated. In the non-boundary-fitted meshes, the elements are not conforming to the domain boundaries and the boundary nodes which are used in the traditional finite element method for the application of boundary conditions no longer exist. Therefore, special techniques are needed for computation of the stiffness matrix of boundary intersecting elements and application of boundary conditions.The stiffness matrix of boundary intersecting elements are calculated via integration of strain energy over the internal parts of these elements. Essential boundary conditions are applied using penalty function method. To examine the effectiveness of the proposed method, some numerical examples are solved and results are compared with those obtained using the standard finite element method.

In this paper the dynamic behavior of a rotating system which includes rotor (shaft), ball bearing and disk in stationary condition and different speeds is investigated. There are nonlinear characteristics in these systems which cause the linear modeling is not sufficiently accurate. So, in this paper the nonlinear dynamic equations of the system are derived and solved. To derive the equations of the system, Hamiltonian method is used, and complex coordinate transform is used to reduce the number of equations. After solving the equations, to investigate the vibrational properties of the system, time response diagram, dynamic orbit, frequency response, and mode shape of the rotor is plotted. To validate the analytical results, finite element method by ANSYS (workbench) software is used.There is a good conformity betweenthe analytical results and finite element results in resonance frequencies of the system in the first three modes which indicates the sufficient accuracy in nonlinear modeling. It can be concluded from nonlinear modeling that the decay rate is negative for the all modes which is indicates the stability of the all modes. Also, the maximum vibration amplitude in the bearing and rotor occurs in third and second modes respectively. Unbalance phase difference of 90 degrees in two discs causes the excitation of all three frequency modes, whereas by unbalance phase difference of 0 or 180 degrees in two discs,only the odd modes (first and third) and the even modes (second) is excited respectively.

In this article، nonlinear axisymmetric bending analysis of sandwich circular plates with homogeneous face sheet and functionally graded core subjected to thermo - mechanical loads is presented. The formulations are based on first-order shear deformation plate theory (FSDT) and large deflection von Karman equations. The nonlinear equilibrium equations are solved using the dynamic relaxation (DR) method combined with the finite difference discretization technique. Material properties are compare to be temperature-dependent and temperature-independent. In order to verify the current work some obtained results are compared with Abaqus finite element method. Finally، The influences of material grading index، boundary conditions،tempresure، core-to-face sheets thickness ratio on the results are studied in detail. Also، in order to investigate the differences between the linear and nonlinear solutions some results are presented based on both linear and nonlinear analysis. Some results indicate that variation of core-to-face sheets thickness ratiohas greater effect on the results of annular geometry compared to circular one.

In this article، nonlinear bending analysis of sandwich circular plates with functionally graded face sheets subjected to transverse mechanical load is presented. The formulations are based on first-order shear deformation plate theory (FSDPT) and large deflection von Karman equations and nonlinear equilibrium equations solved by the dynamic relaxation (DR) method combined with the finite difference discretization technique. In order to verify the current work some obtained results are compared with the solutions reported in the literature and Abaqus finite element method. Finally، The influences of material constant k، boundary conditions، core-to-face sheets thickness ratio on the results are studied in detail.

The average behavior of composite material like masonry can be described in terms of the relation average stresses and strains (macro model) if the material is assumed to be homogeneous. The average stress-strain relationship can be determined generally using two approaches. A possible approach is experimental investigation from the available experimental data. Another approach, adopted in this resedrch, is to develop a linear homogenization technique, which describes the behavior of the masonry from the geometry and the behavior of the representative basic cell. In this research, the elastic properties of a basic cell in masonry with a periodic arrangement of blocks were obtained based on a local stress field approach (micro-modeling of the mortar and blocks).Two different methods were used for computing the equivalent orthotropic elastic properties of the basic cell as a continuum, the approximate energy method (a closed form solution) and the finite element based method. The finite element method was used to approximately find the orthotropic yield curves of the homogenous element. The similarity of the general behavior of these gied curves with regard to the experimental facts was considerable.